The present invention relates generally to biodegradable polymers. More particularly, it concerns biodegradable polymer blends containing oligomeric esters and use of such blends in the production of shaped polymeric objects having improved properties which do not diminish over time.
There has been considerable interest in recent years in the use of biodegradable polymers to address concerns over plastic waste accumulation. The potential worldwide market for biodegradable polymers is enormous (>10B lbs/yr). Some of the markets and applications most amenable to the use of such biopolymers range from single use applications, which can include packaging, personal hygiene, garbage bags, and others where the biopolymers become soiled and are ideally suited for biodegradation through composting, to markets and applications in which the biopolymers can be recovered as clean materials, such as garment bags, shopping bags, grocery bags, etc. and are suitable for recycling, as well as composting, or biodegradation in landfills.
Polyhydroxyalkanoate (PHA) biopolymers are thermoplastic polyesters, many of which can be produced by microorganisms in response to nutrient limitation. The commercial potential for PHA's spans many industries, and is derived primarily from certain advantageous properties which distinguish PHA polymers from petrochemical-derived polymers, namely excellent biodegradability and natural renewability.
Widespread use and acceptance of PHA's, however, has been hindered by certain undesirable chemical and physical properties of these polymers. For example, PHA's are among the most thermosensitive of all commercially available polymers. As such, the rate of polymer degradation, as measured by a decrease in molecular weight, increases sharply with increasing temperatures in the range typically required for conventional melt-processing of PHA's into end-products such as films, coatings, fibers etc. An additional limitation of the potential utility of PHA polymers relates to the observation that some polymer characteristics, for example ductility, elongation, impact resistance, and flexibility, diminish over time. This rapid “aging” of certain PHA-derived products is unacceptable for most commercial applications. Thus, the success of PHA as a viable alternative to both petrochemical-derived polymers and to non-PHA biodegradable polymers, will depend upon novel approaches to overcome the unique difficulties associated with PHA polymers and with products derived therefrom.
The blending of two or more polymers has become an increasingly important approach for improving the cost performance of commercial plastics. For example, blending may be used to reduce the cost of an expensive engineering thermoplastic, to improve the processability of a high-temperature or heat sensitive thermoplastic, to improve impact resistance, etc. Therefore, blending is one approach which has the potential to provide new classes of biodegradable PHA-containing polymers having unique and improved properties. In this way, it may be possible to overcome the limitations of PHA compositions that have limited their widespread industrial utilization while retaining their desirable features. Unfortunately, many polymers are immiscible when blended, and result in undesirable phase separation during processing. Generally, such blends of incompatible or thermodynamically immiscible polymers exhibit poor mechanical properties and processing difficulties.
Compatibilizing compounds have been identified and developed for numerous polymer systems. These compounds can reduce interfacial tension and thereby promote miscibility of otherwise poorly miscible polymers. The availability of compatibilizers provides an effective means by which polymeric compositions can be produced. However, with PHAs, very little has been achieved in this regard, and there is a need for the identification of compounds providing effective compatibilization of blends containing different PHA polymers or blends containing PHA and non-PHA polymers.